Security supports comprising at least one security element such as a security thread or stripe or patch are well known for making security documents in particular valuable documents such banknotes, cheques, vouchers or identity papers/cards.
Optically variable effects generating structures are widely known and used as security features. These structures are commonly formed as relief structures, reflection structures, reflection gratings, holographic structures, and the like, in a substrate, which is then provided with a reflective coating, for example a continuous or partial metallic layer to enhance the optically variable effect.
The most often security elements comprising these structures, which are in form of a patch or stripe, are then adhered to a support for making the article or document which is to be secured. Alternatively, the security element can be a thread partially embedded in the support, the optically variable effects being visible in a window.
WO 02/00446 discloses a security device comprising a substrate formed with a surface relief defining an optically variable effect generating structure and at least two different reflection enhancing materials, which are provided on, or on the same side of the substrate with respect to, the surface relief. The optically variable effect can be viewed against a background defined by the reflection enhancing materials.
These security devices display optically variable effects which have their diffraction spectrum spatially modulated by the reflective hue of the underlying metallic pattern. This metallic pattern is formed by two different metallic layers and cannot be easily matched by dyeing or colouring material layers.